Subsea wellheads commonly include hangers for the support of strings of casing which extend down into a well. It is necessary for at least some hangers, particularly a production casing hanger, to be provided with pack-off seals. Such a pack-off is usually inserted in a wellhead by means of a running tool inserted into the wellhead bore. In current practice, the aggregation of tolerances in the complex interface between the tool, a pack-off, a casing hanger and the wellhead is liable to lead to uncertainty of the proper setting of the pack-off.
The present invention accordingly particularly relates to an assembly which provides a simple and reliable interface between a pack-off and a running tool and, more particularly, an interface which ensures the accurate location of the pack-off before it released from the tool. A further aim of the invention is to eliminate the need for a retrieval ring on the running tool for unset pack-offs.